Marker-Assisted Selection: Current Status and Future Perspectives in Crops, Livestock, Forestry and Fish
by FAO
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Since almost the beginning of human civilization, exploiting variation in the characteristics of the plant and animal genetic resources that are used for producing food and other agricultural products through breeding has been at the heart of efforts to increase and diversify agricultural production and productivity, enhance food security and incomes, and adapt farming to changing environmental conditions and social needs. Initially, this was achieved simply by selecting and reproducing preferred individuals or spontaneous variants, and indeed this practice remains important today as the basis for producing new generations of cultivated landraces and indigenous breeds. However, the crops, trees, livestock and fish that are farmed today have arisen largely from the introduction of scientific breeding at the beginning of the twentieth century, with the inclusion of crosses into breeding schemes prior to artificial selection and application of Mendel’s laws of inheritance to improve both simple and quantitative traits providing the foundations for modern genetics.
Today, thanks to continuing investments made in research and technology development, the process of producing improved varieties, clones, breeds and strains of agriculturally important species has become progressively more accurate, reliable and efficient. Nevertheless, one of the continuing technical constraints to more effective breeding is that selecting material with one or a combination of the characteristics required by farmers, foresters, industry and consumers still relies mainly on physical and agronomic attributes (phenotype). Some of these characteristics are influenced by the environment and are therefore not necessarily a good guide to the actual heritable genetic composition (genotype) of the material in question. Others may not be visible or may only be detected in mature plants and animals. Others again may be difficult or very costly to screen, and many characters such as drought tolerance and milk composition are controlled by a large number of genes whose mode of action as well as their interaction with each other and with various environmental triggers is mainly unknown. Improving the identification, selection and monitoring of specific characters in plants and animals through breeding schemes is therefore a critical need to secure future improvements in genetic resources for food and agriculture.
Since the first description of DNA structure over 50 years ago, scientists have made tremendous strides in identifying genes and gene functions, making it increasingly possible to detect genetic differences (DNA polymorphisms) for traits among individual plants and animals in a much more direct way, thereby assisting in the selection of desired traits. The central technology involved is molecular markerassisted selection (MAS), using sequences and/or banding patterns of DNA that have been shown through linkage mapping to be located in or near genes that affect the phenotype. These molecular markers can then be used to assist breeders track whether the specific gene or chromosome segment(s) known to affect the phenotype of interest is present in the individuals or populations of interest.
Although the ultimate goal of identifying the location, function and most favourable alleles of each gene through genome sequence and post-genomics research, and then using markers to select for economically important genes in breeding programmes, is still decades away, in recent years the use of MAS in agriculture has moved progressively from theory to practical application. In the process, it has generated both high expectations for increasing genetic progress through breeding, and raised a number of unresolved challenges. These include: selection of the most appropriate methods and tools for MAS among the many now available for the task at hand, analysing and managing the data produced given the increasing trend towards highthroughput techniques and the constraints imposed by suboptimal levels of resources currently attached to breeding and science and technology including biotechnology, and dealing with intellectual property rights, especially in developing countries.
Since its foundation, FAO has recognized that the biological basis for sustainable agricultural production, fighting hunger and world food security lies in the genetic resources used for food and agriculture. It has also recognized the enormous contributions that have been made to the improvement of these resources through both traditional and more advanced breeding, as well as the ever-increasing role played by biotechnology in improving breeding processes and products. As a knowledge organization, one of FAO’s major roles is to provide its Members and their institutions with factual, comprehensive and current information relevant to sound stewardship of crops, livestock, forestry and fisheries, thereby ensuring its availability as a global public good. This book, by providing a comprehensive description and assessment of the use of MAS for increasing the rate of genetic gain in crops, livestock, forestry and farmed fish, including the related policy, organizational and resource considerations, continues the Organization’s tradition of dealing with issues of importance to agricultural and economic development in a multidisciplinary and cross-sectoral manner. As such it is hoped that the information and options presented and the suggestions made will provide valuable guidance to scientists and breeders in both the public and private sectors, as well as to government and institutional policy- and decision-makers.